Limit-gage for screws.



J. BARIQUAND. LIMIT GAGE FOE sonnws. APPLICATION FILED SEPT. 13, 1909.

Patented Mar. 28 1911.

3M a i 1 mfimm THE NORRIS EETERS co., WASHINGTON. n. c.

JULES BARIQUAND, OF PARIS, FRANCE.

' LIMIT-GAGE FOR SCREWS.

To all whom it may concern:

Be it known that I, JULEs BARIQUAND, a citizen of the French Republic,and resident of Paris, France, have invented certain new and usefulImprovements in Limit-Gages for Screws, of which the following is aspecification.

The international system of screws and nuts adopted by the congress ofZurich in conformity with the researches of the Socit dEncouragementpour lIndustrie Nationale en France, defines the shape and the pitch ofthe screw threads which correspond to the various diameters of screwsand establishes as a principle the general rule that the theoreticalprofile of the screw threaded part is a profile limited between thescrew and its corresponding nut. The screw, when practically constructedfor the requirements of the current mechanics, consequently must alwaysbe smaller or at the highest equal to the standard screw made accordingto the theoretical limit profile and on the other hand, the screwthreaded nut or the tapped hole must in practice always be larger or atthe least equal to the standard nut manufactured according to the samelimit profile. But the screws which are currently employed in mechanicalconstruction must, besides, fulfil another condition which is that ofinterchangeability.

In order to be able to be termed interchangeable a mechanical part ormember, must have its dimensions all comprised between the maximum andminimum limits,

. which may be narrow or wide according to requirements and which aredetermined by practice in such a manner that the said member may bereplaced in the mechanism of which it forms a part, by another membertaken indiscriminately from the series manufactured and this without itbeing necessary to make any adjustment or other operation than that ofsimply putting the member in lace. p The difference between the maximumand the minimum in the dimension of a part of manufactured andinterchangeable mechanical members is called allowance. It is needlessto say that the greater the allowances are the more easily the membersare made. But on the other hand the easiness of execution must only betaken into consideration after the conditions which are required for thegood execution of the mechanisms of which the interchangeable mem-Specification of Letters Patent.

Application filed September 13, 1909.

Patented a. 28, 1911.

Serial No. 517,430.

bers form a part. In order to apply these rules of theinterchangeability to the screws and as the international system definesthe maximum profile, it remains to define the minimum. The question isbeing examined by the Socit dEncouragement cited above, However, forcarrying out these researches and also for easily applying the ruleswhich will be given, the work shops are now wanting a commodiouscontrolling implement for examining a manufactured screw and forascertaining instantaneously if the dimensions of the screw threadedpart of this screw are comprised in the allowance forinterchangeability. It is for filling up this gap that the limit screwgage forming the subject matter of the present invention has beendevised.

In the accompanying drawing: Figure 1 is a side elevation View of thelimit screw gage; Fig. 2 shows a diagram illustrating the principle ofthe gage. Fig. 3 is a front elevation view of the gage;

This gage comprises two jaws 10 and 11 which are connected together atone of their ends by a hinge 12 and at the other end by means of a screw13 on which a graduated barrel button 14. is screwed.

The hinge may be of any well known constructions for compasses such asarticulation, knuckle joint, spring and so on. Reserving the use of anyone of the well known systems referred to, I have shown in the exampleillustrated by the drawing, a connection by means of a flat spring 12rigidly secured to each of the jaws by means of a screw 15 and of asafety pin 16.

In order to oblige the jaws to open and close correctly without turningto one side or the other (casting), a member 17 which is narrower thanthe jaws is provided at the end of the jaws opposite the hinge. Thismember or tongue 17 is secured in a groove of one of the jaws by meansof the screw 18 and is adjusted with a close fit into a correspondinggroove of the other jaw so as to be able to move in the latter. Thismember 17 carries a heel 19 which limits the opening of the jawsaccording to the clearance left at the point 20 and the said heel 19 ofthe tongue 17. In the implement thus combined, a hole has been providedbetween the two jaws at a point 21 of the line of contact between thesaid jaws. The said hole is tapped for the maximum limit profile of thescrew for the diameter chosen D and this when the two jaws are as wideopen as possible, the barrel knob being at zero.

It is readily understood that when the jaws are closed by means of thebarrel knob screwed on the screw 13 which is rigidly connected with theaw 11 and is locked in place by means of the set screw 21, thegraduations of the barrel knob move relatively to an index engraved intothe upper jaw 10 and thus give an indication of that amount by which thehole 21 in the jaws varies from the hole formed therein originally atnormal position of the jaws. The possible minimum will be attained whenowing to the action of the scale barrel knob the two jaws will have beenapplied upon each other.

As readily seen the two limit positions of the implement in an openstate and the implement in a closed state can by a suitable adjusting bemade to correspond to the maximum and the minimum of the allowance ofthe interchangeability of the screw considered.

All the screws having the nominal diameter D must first be able to beengaged in the implement when the latter is in an open state, whichcorresponds to the maximum limit. Those which cannot be engaged must atonce be discarded. Among the screws which can be engaged in the tappedhole when the gage is open, two cases can occur for a screw tested bythe gage: 1. hen the scale knob is rotated, the contact between the jawsand the said screw will take place before the control limit gage beclosed and, in this case, the screw will have a good interchangeability.2. The jaws can be brought into a contact with each other without thescrew being tightened in the hole 21 and in this case the screw has tobe rejected as being too small.

In the drawing it is indicated that the measuring aperture D engages thescrew to be gaged by means of three chasers 7, 8, 9, preferablyequidistantly distributed on the inner circumference of the hole. It isobvious that the gaging circle is a circle, the periphery of which isdefined by these chasers; the wall portion of the hole D between theprojecting chasers may be recessed as shown. It is also obvious that acomplete circular circumference may be used as a gaging aperture insteadof three projecting points. In the latter case the gage would measurethe length of a diameter of the inserted threaded member.

The employment of these chasers is based upon the following theoreticalprinciple, illustrated by Fig. 2 in which D and d designate thediameters of two circumferences which out each other along a chord A B,C being the middle of A B, the line C is perpendicular to A B.Designating the half of chord A B by K and by H and it the distances ofA B from the points E and 6 respectively of the diameter through C inboth circumferences, and by m the differ ence between H and h, we areable to explain, the ditference between the diameters D(Z:m as afunction of m D H and we have:

K :I I(Dl-I):h(cZ-h). Then replacing 7L by H-m and (Z by D-w theequation becomes H (D H) (Hm) (DarH[-m) and gives If one chooses for A Bthe chord corresponding to the side of the equi-lateral triangleinscribed in the circumference D so marks-g D the equation becomes inthis particular case:

and if m is very small in comparison with D we will have a greatapproxnnation by In the gage shown by Fig. 1 the tapped hole 21 has beenhollowed out so as to leave in this hole three chasers 7, 8, 9representing the theoretical limit profile of the screw thread, thesethree chasers being positioned at the summits of an equilateraltriangle. The stationary jaw 11 contains the two chasers 8 and 9 whichcorrespond to the points A and B of the geometrical figure (Fig. 2)while the movable jaw 10 contains the chaser 7 which corresponds to thepoint E so that its measured movements give the value of m.

By graduating in a suitable manner the tale knob 14 which graduation ismade by taking into account the lever arms from the hinge to the hole 21and to the screw of the scale knob, the pitch of this screw 13 as wellas the theoretical principle explained above, the action of the operator011 the scale knob will allow to read directly the value of the diameterof the screw considered.

According to the degree of sensibility which one desires to give thegage, the scale knob lei could be provided with a frictional device ofany of the well known constructions and adapted to replace the variableaction of the hand by the constant action of a mechanical device.

The inventor has also devised a gage for the same use in which threechasers have been provided in at 120 degrees from each other in a ring,one of these chasers being actuated by a screw gage, but theconstruction of this instrument is less simple and less practical thanthat of the gage described above and shown by the drawing.

Having now fully described my said invention what I claim and desire tosecure by Letters Patent is 1. In a thread gage the combination of apair of jaws, a plate detachably fastened to said jaws and resilientlyconnecting said jaws at one end thereof, said jaws being provided withsections of tapped apertures which supplement each other to form atapped circular aperture of standard size when said jaws are at acertain position with respect to each other, a micrometer screw threadedinto one of said jaws and extending through both of said jaws and a nutengaging said screw, and resting against the other aw said nut beingprovided with a scale for indicating the variation ,of said aperturefrom standard size.

2. In a thread gage the combination of a pair of jaws, a leaf springconnecting said jaws at one end thereof, pins extending through saidleaf spring and into said jaws, said jaws being provided with sectionsof tapped apertures which supplement each other to form a tappedcircular aperture of standard size, when said jaws are at a certainposition with respect to each other, a micrometer screw secured in oneof said jaws and extending loosely through the other aw, a nut engaglngsaid screw and said other aw, said nut being provlded with a scale forindicating the variation of K said aperture from standard size.

3. In a thread gage the combination of a pair of jaws, a leaf springconnecting said jaws at one end thereof, said jaws being provided withsections of tapped apertures which supplement each other to form acircular aperture of standard size when said jaws are at a certainposition with respect to each other, a micrometer screw secured in oneof said jaws and loosely extending through the other aw, a nut engagingthe loose end of said screw and said other jaw and being provided with ascale for indicating the deviation of said aperture from standard size,each of said jaws being provided with a groove said grooves being inalinenient with each other, a guiding member fastened to said other jawand resting in said grooves, said member being pro vided with aprojecting portion for limiting the distance between said jaws.

In testimony whereof I have hereunto set my hand in presence of twowitnesses.

J ULE S BARIQUAND. lVitnesses H. C. Coxn, JOHN BAKER.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. 0.

